This invention relates to a refrigerant circuit for an ice making machine and the like, in which, when a high-pressure and high-temperature vaporized refrigerant is fed from a compressor to an evaporator so as to release the ice formed on ice making plates and the like, drop in the performance of the compressor and occurrence of troubles in the compressor are designed to be prevented by reducing, as necessary, the pressure on the refrigerant outlet side of the compressor.
An ice making machine for making automatically a number of ice pieces has a freezing circuit for circulating a refrigerant, in which the ice making plates are designed to be heated by feeding a high-pressure and high-temperature vaporized refrigerant (hereinafter sometimes referred to as hot gas) from a compressor to an evaporator attached to the ice making plates, upon switching from a freezing operation to an ice releasing operation, to accelerate releasing of the ice pieces formed on the ice making plates. For example, FIG. 3 shows a flow-down system ice making machine, in which water to be frozen is sprinkled against ice making plates standing perpendicularly to form ice pieces continuously thereon. In this type of ice making machine, an evaporator 14 led out of a freezing circuit 12, shown in FIG. 4, running zigzag in the transverse direction is secured in closed contact between a couple of ice making plates 10 disposed perpendicularly, and a refrigerant is circulated during a freezing operation to forcibly cool these ice making plates 10. A plurality of vertical elongated ridges 10a are arranged on the freezing surface of each ice making plate 10 in the transversal direction, and ice pieces 16 are designed to be formed between every two adjacent ridges 10a at the positions where the evaporator 14 runs. A slanted water collecting plate 18 having a plurality of through holes 18a is disposed immediately below the ice making plates 10, and the portion of the water to be frozen which, was fed to the ice making plates 10 during the freezing operation but failed to freeze is dripped through the through holes 18a to be recovered and stored in a water tank 20 locating below the water collecting plate 18. Incidentally, the water collecting plate 18 also serves to guide the ice pieces 16 released under an ice releasing operation and dropped thereto into an ice bin 22 disposed diagonally below the water collecting plate 18.
A water supply pipe 26 led out of the water tank 20 through a circulating pump 24 is connected to a sprinkler 28 disposed above the ice making plates 10 and on the freezing surface sides thereof. A plurality of water distribution holes (not shown) are formed in this sprinkler 28, and the water to be frozen pumped from the tank 20 during the freezing operation is designed to be sprinkled through these water distribution holes onto the freezing surfaces of the ice making plates 10 cooled to the freezing point and to flow down therealong, whereby to form ice pieces 16 having a predetermined shape on the freezing surfaces.
FIG. 4 shows schematically a constitution of the freezing circuit to be suitably employed in the above-described automatic ice making machine. The freezing circuit 12 essentially has a compressor 30 for compressing a refrigerant such as Freon (a fluorinated hydrocarbon) a condenser 32 to which the high-pressure and high-temperature vaporized refrigerant obtained after compression in the compressor 30 is fed, an expansion valve 34 to which the refrigerant condensed to be liquefied in the condenser 32 is fed and an evaporator 14 to which the refrigerant expanded to be vaporized through the expansion valve 34 is fed. The evaporator 14 performs heat exchange with the refrigerant expanded and vaporized through the expansion valve 34 so as to cool the ice making plates 10 attached to the evaporator 14 below the freezing point and allow the water to be frozen flowing down along the ice making plates 10 to freeze gradually. The vaporized refrigerant heated after heat exchange in the evaporator 14 is fed back to the compressor 30, compressed to a high pressure and a high temperature and then recirculated. Incidentally, the reference number 36 denotes a detecting means for detecting the temperature of the refrigerant on the refrigerant outlet side of the evaporator 14, and the detecting means 36 is designed to perform aperture control of the expansion valve 34.
A pipe 38 branching out of a pipe 37 located on the outlet side of the compressor 30 is connected through a hot gas valve 40 such as a solenoid valve to the inlet side of the evaporator 14 to constitute a so-called hot gas circuit 42. The hot gas valve 40 is closed during the freezing operation to interrupt circulation of the refrigerant through the hot gas circuit 42 and to circulate the refrigerant to the freezing circuit 12 only. Meanwhile, when the ice releasing operation for releasing and dropping the ice pieces is started after completion of the freezing operation at the ice making plates 10, the hot gas valve 40 is let open to allow a hot refrigerant (hot gas) to circulate through the hot gas circuit 42. Thus, the ice making plates 10 attached to the evaporator 14 are heated to release adhesion of the ice pieces 16 formed on these ice making plates 10 and allows them to drop by their own weight.
As described above, when the operation mode of the ice making machine is switched to the ice releasing operation, the hot gas valve 40 is changed over from the closed posture to the open posture (1) to interrupt circulation of the refrigerant through the freezing circuit 12 and (2) to feed the high-pressure and high-temperature vaporized refrigerant from the outlet side of the compressor 30 to the evaporator 14. However, as shown in FIG. 4, no closing means such as a valve is disposed to the inlet side of the condenser 32. Accordingly, the hot gas delivered from the compressor 30 during the ice releasing operation is not entirely fed to the hot gas circuit 42, but the substantial portion of the hot gas is designed to be circulated through the hot gas circuit 42. The small portion of the hot gas flows into the condenser 32 where the heat of the hot gas is dissipated well, and the hot gas is liquefied and stays therein (this phenomenon is termed as "stagnation"). If some portion of the hot gas stagnates in the freezing circuit 12 connected to the condenser 32, the hot gas to be circulated through the hot gas circuit 42 decreases with time corresponding to the amount of stagnation. It can thus be pointed out that the ice releasing performance in the evaporator 14 is gradually lowered to require a considerable time for the ice releasing operation, disadvantageously. Such problem occurs conspicuously when the ambient temperature is low. Incidentally, in the freezing circuit of the system in which a receiver is provided on the outlet side of the condenser 32, the-amount of stagnated hot gas is increased, so that the ice releasing performance is further lowered.
In the above ice making machine, the temperature rise at the ice making plates 10 brought about by the dropping of the ice pieces 16 therefrom by the ice releasing operation is designed to be detected by a thermostat (not shown) so as to switch the operation mode from the ice releasing operation to the freezing operation. When the amount of the hot gas circulated through the hot gas circuit 42 is decreased due to the reason described above, the ice pieces 16 formed on the ice making plates 10 fail to be released evenly, but those ice pieces 16 formed near the thermostat occasionally drop sooner. In such cases, the operation mode is switched from the ice releasing operation to the freezing operation, although the ice pieces 16 formed at the other portions have not yet been dropped, leading to double-freezing, disadvantageously.
A countermeasure for such problem is proposed, in which a solenoid valve 44 is disposed, as shown in FIG. 5, on the downstream side (on the condenser (32) side), with respect to the flow of the refrigerant, than the junction of the pipe 38 with the pipe 37 connecting the compressor to the condenser 32. Namely, during the freezing operation, the solenoid valve 44 is let open to allow the refrigerant to circulate through the freezing circuit 12, and also the hot gas valve 40 is closed to interrupt circulation of the refrigerant through the hot gas circuit 42. Meanwhile, when the operation mode is switched from the freezing operation to the ice releasing operation, the solenoid valve 44 is closed to interrupt circulation of the refrigerant through the freezing circuit 12, and also the hot gas valve 40 is let open to allow the heated refrigerant (hot gas) to circulate through the hot gas circuit 42. Thus, the hot gas delivered from the compressor 30 during the ice releasing operation is entirely fed to the hot gas circuit 42 so as to prevent drop in the ice releasing performance, enabling reduction of the time required for the ice releasing operation.
However, if the solenoid valve 44 is closed when the operation mode of the ice making machine is switched to the ice releasing operation and the ice releasing operation is continued in such state, the pressure on the outlet side of the compressor 30 sometimes increases greatly. Namely, upon mode switching from the freezing operation to the ice releasing operation, the hot gas valve 40 is let open to swiftly lower the pressure on the outlet side of the compressor 30, and the pressure on the inlet side of the evaporator 14 is increased. The reason is that the aperture of the hot gas valve 40 is set relatively great, and the solenoid valve 44 is closed simultaneously or with a predetermined time lag to allow a large amount of hot gas to circulate through the hot gas circuit 42 only. At the initial and intermediate stages of the ice releasing operation, a number of ice pieces 16 adhere firmly onto the ice making plates 10, and even if a large amount of hot gas is circulated through the evaporator 14, the heat is consumed for melting the frozen surface between the ice pieces 16 and each of the ice making plates 10. Meanwhile, the pressure on the inlet side of the evaporator 14 is elevated by the hot gas already flowed thereto in a large amount, so that the hot gas is not only cooled but also liquefied (e.g., in the case of Freon R-22, it is condensed at 0.degree. C. or higher, if the pressure exceeds 4 kg f/cm.sup.2 G) and fed back as such to the compressor 30, and thus the refrigerant repeats the cycle described above.
At the final stage of the ice releasing operation, since most of the ice pieces 16 are released from the ice making plates 10, the temperature drop of the hot gas to be brought about by the heat exchange becomes small, and the amount of liquefied hot gas is reduced to increase the pressure at the inlet side of the evaporator 14. Accordingly, the delivery of the hot gas from the compressor 30 increases, so that the pressure on the outlet side of the compressor 30 is increased. Namely, the cycle that the pressure on the inlet side of the evaporator 14 and the pressure on the outlet side of the compressor 30 are increased acceleratively by the increased amount of the hot gas passing through the hot gas valve 40 is repeated (sometimes to extremely high values, e.g., 7 kg f/cm.sup.2 G on the inlet side of the evaporator 14; 23 kg f/cm.sup.2 G on the outlet side of the compressor 30). If the pressure on the outlet side of the compressor 30 is thus increased, drop in the performance is caused due to the load applied to the compressor 30, and accidents such as burning, damage, etc. are liable to occur.
Incidentally, since the temperature at which the refrigerant is liquefied becomes higher as the pressure is increased, the refrigerant is easily liquefied at the final stage of ice releasing operation due to the rise of the pressure in the condenser 33 in the freezing circuit shown in FIG. 4, as described above, and thus the amount of stagnated refrigerant is much greater.
This invention is proposed in view of the problems inherent in the prior art refrigerant circuits for ice making machines and the like, as described above, and in order to overcome them successfully, and it is an objective of the invention to provide a means which can prevent drop in the performance of the compressor or occurrence of burning etc. when the ice pieces grown on the ice making plates and the like are to be released by circulating a hot vaporized refrigerant (hot gas) to the evaporator.